The invention is based on patent application No. 10-334728 Pat. filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical recording medium which is used for recording and/or reproducing information using predetermined light, and also relates to a method of making the optical recording medium and an optical memory device using the optical recording medium.
2. Description of the Background Art
An optical recording medium is used for recording and/or reproducing information, and is adapted to allow the information recording and/or reproducing by emitting predetermined light thereto. These recording and reproducing with the predetermined light are performed by an optical memory device.
In such an optical memory device, a head for information recording emits a predetermined light spot to an information recording region on the optical recording medium so that information may be recorded (i.e., written) on the optical recording medium. Depending on the kind of the optical recording medium, the recording can be performed reversibly and, in other words, erasably (i.e., to allow rewriting of the information on the optical recording medium), or the recording can be performed irreversibly and, in other words, unerasably (without rewriting of the information on the optical recording medium). For reproducing (reading) information from the optical recording medium, a head for information reproduction emits a light spot to the information recording region of the optical recording medium.
In either of the above cases, the optical recording medium is moved relatively to the head provided for recording and/or reproducing the information, and the head emits the light spot onto the optical recording medium for recording or reproducing the information. In the case of, e.g., the optical recording medium having a disk form, the head is arranged in the predetermined position on the optical recording medium, and the head emits the light spot to the predetermined position (track) on the recording medium surface for recording or reproducing the information while keeping rotation of the recording medium. In this emitting operation, the light spot must be maintained at the predetermined position (track) on the recording medium surface.
For maintaining the light spot at the predetermined position (track) on the recording medium surface during the light emission, the recording medium surface is provided with a tracking pattern (i.e., tracking guide such as a guide groove) forming an index of the light spot position. This tracking guide is provided for the purpose of stably recording or reproducing information even if an eccentric motion or deviation from a perfect circle occurs in position on the recording medium, where the information is to be recorded or reproduced, due to rotation of the optical recording medium having, e.g., a disk form.
In an optical memory device which uses the optical recording medium provided with the tracking guide, the tracking pattern (tracking guide) is always tracked (followed) so that the light spot may always be located on the track of the recording medium where the information is to be recorded or reproduced. For accurate tracking, the tracking servo is performed, e.g., in the case where the optical recording medium has the disk form. In this tracking servo, a shift of the tracking guide, e.g., in the radial direction of the disk, which may occur due to rotation of the disk, is detected, and the position of the light spot is automatically controlled in accordance with the shift so that the light spot may always be emitted to the track on the optical recording medium.
The tracking servo can be classified into continuous servo system using a continuous tracking guide (e.g., groove) and a sample servo system using spaced tracking guides (e.g., pits). The continuous servo system can be classified into the push-pull type and the three-beam type.
In the continuous servo system of the push-pull type, the optical recording medium is provided with a tracking guide (guide groove) having a V-shaped section, and the light spot is emitted to the guide groove on the recording medium. The amount of light reflected from the guide groove is detected to determine a distribution of the light intensity by a multidevided photo detector, and the tracking is performed so that the measured light intensity distribution may be constant.
In the continuous servo system of the three-beam type, the optical recording medium is provided with a tracking guide formed of, e.g., signal pits. Three light spots, which are aligned in a direction inclined with respect to the track direction, are emitted to the signal pits on the recording medium. Amounts of light reflected from the respective signal pits are detected, and the tracking is controlled so that the amounts of the light reflected from the signal pits on the opposite ends may be equal to each other.
In the sample servo system, the optical recording medium includes a tracking guide provided with pattern groups which are spaced from each other by a predetermined distance. Each pattern group is formed of two signal pits, which are shifted from each other, e.g., in the tracking direction and are shifted slightly laterally with respect to the center of the track. The light spot is emitted to the pattern group on the recording medium, and the intensities of the light reflected from the pattern group (two signal pits) are detected. The tracking is controlled so that the reflectances determined by these two signal pits may lower by the same magnitude.
All of these types utilize the tracking guide (tracking pattern) having a surface at a level shifted from that of an information recording region. More specifically, the continuous servo system of the push-pull type utilizes the tracking pattern formed of a groove having a V-shaped section, and the continuous servo system of the three-beam type and the sample servo system utilize the tracking pattern of signal pits.
In addition to the above, such a tracking pattern may be utilized that requires neither groove nor pit on the optical recording medium. For example, Japanese Laid-Open Patent Publication No. 7-296361 has taught tracking servo for a magnetic recording medium, in which an optical pattern (i.e., a tracking layer) containing a dye for tracking servo signals is arranged under a magnetic layer for magnetic recording, and the tracking servo is performed using the optical pattern.
An object of the invention is to provide an optical recording medium, which is used for recording and/or reproducing information by predetermined light, and allows accurate tracking of a tracking pattern during recording and/or reproducing of the information, compared with a conventional optical recording medium having a tracking pattern which is formed of, e.g., a groove or pits and may cause a larger making error. It is also an object of the invention to provide a method of making such an optical recording medium.
Another object of the invention is to provide an optical recording medium, which is used for recording and/or reproducing information by predetermined light, and can keep a predetermined distance between the optical recording medium and the head or probe provided for information recording and/or reproducing while performing accurate tracking of the tracking pattern even in the case where the predetermined light must be emitted from the position near the optical recording medium for recording and/or reproducing of the information and, for example, in the case of near-field light recording and reproducing of information utilizing near-field light (evanescent light). It is also an object of the invention to provide a method of making such an optical recording medium.
Still another object of the invention is to provide an optical memory device which utilizes near-field light (evanescent light) for performing near-field light recording of information onto the optical recording medium and/or near-field light reproducing of information from the optical recording medium, or an optical memory device which utilizes the near-field light (evanescent light) only for performing near-field light reproduction. More specifically, the object of the invention is to provide the optical memory device which can perform recording and/or reproducing of information while performing accurate tracking of the tracking pattern of the optical recording medium accommodated in the device and performing control to keep a required space between the optical recording medium and the head or probe provided for information recording and/or reproducing.
The invention provides an optical recording medium, a method of making the same and an optical memory device described below.
An optical recording medium including:
a substrate;
an information recording region arranged on the substrate and capable of bearing information being readable with predetermined light; and
a tracking region arranged on the substrate, having optical characteristics different from those of the information recording region and having substantially no difference in level with respect to the surface of the information recording region.
A method of making an optical recording medium, including the steps of:
forming uniformly a recording layer on a substrate, the recording layer being made of a recording material being reversibly reactive to predetermined light; and
causing an irreversible reaction in a partial region of the recording layer without causing a substantial difference in level with respect to the other region of the recording layer.
(1) An optical memory device including:
an optical recording medium having a recording layer, and allowing recording and/or reproducing of information with respect to the recording layer with near-field light (evanescent light), the recording layer including an information recording region and a tracking region having substantially no difference in level with respect to the surface of the information recording region;
an exposing device having a head for emitting the near field light (evanescent light) to the optical recording medium;
a drive device for driving the head; and
a control device for controlling the drive device to perform tracking of the head in accordance with the tracking region.
(2) An optical memory device for accommodating an optical recording medium, and utilizing near-field light (evanescent light) for performing near-field light recording of information onto the optical recording medium and/or near-field light reproducing of information from the optical recording medium, the optical recording medium having a recording layer, and allowing recording and/or reproducing of information with respect to the recording layer with the near-field light (evanescent light), the recording layer including an information recording region and a tracking region having substantially no difference in level with respect to the surface of the information recording region, and the tracking region being used for tracking.